1. Field of the Invention
This invention relates to a process for improving the productivity of catalysts used in the continuous gas-phase, fluid bed process for the polymerization of olefins.
2. Prior Art
U.S. Pat. No. 4,414,132 to Goodall et al. teaches the use of highly active, stereospecific catalysts for the polymerization of olefins.
It is known from U.S. Pat. No. 4,065,609 to Willmore that gas phase olefin polymerization conducted in an agitated bed at from 0.1.degree. C. to 5.0.degree. C. of the dew point temperature of the reactants increases stereospecificity and yield of the olefin.
It is also known from Europrean Specification No. 0141461 that productivity of the Goodall catalyst can be improved by pretreating the catalyst with dialkylaluminum chloride. However, the catalyst pretreated in this manner is so highly active that special handling techniques are required in order to introduce it into the polymerization reactor. In addition, if the catalyst is not pretreated with dialkylaluminum chloride before it is introduced into the polymerization reactor, enhanced results are not obtained according to the reference.
Independently conducted experiments have substantiated that little or no improvement is obtained when dialkylaluminum halide is added to the Goodall catalyst in the polymerization reactor under ordinary polymerization conditions. Surprisingly, however, it has now been found that an unexpected increase in catalyst activity is obtained if dialkylaluminum halide is added to the reactor near the dew point temperature of the reactants; this increase is well above that which might be expected by operating at temperatures near the dew point alone.